The present invention relates to a process for the solventless hydrogenation of 4-acetoxyacetophenone and to a process for the low residence time dehydration of 4-acetoxyphenylmethylcarbinol. These processes are useful in improved methods for the production of 4-acetoxystyrene, poly(4-acetoxystyrene) homopolymers, copolymers and terpolymers with 4-acetoxystyrene as one of the monomers, and the hydrolysis of poly(4-acetoxystyrene) to poly(4-hyrdoxystyrene), including hydrolysis of copolymers and terpolymers containing 4-acetoxystyrene.
It is known in the art to produce monomers, homopolymers and copolymers of 4-acetoxystyrene and to hydrolyze the same to produce 4-hydroxystyrene derivatives or poly(4-hydroxystyrene). These compounds may be employed in the production of adhesives, coating compositions, and the like. Poly(4-hydroxystyrene) compounds are useful as binder resins for photoresists. Alpha acetoxystyrene and beta acetoxystyrene are known compounds and are described in U.S. Pat. No. 4,144,063 and acetoxymethylstyrene is described in U.S. Pat. No. 3,963,495. U.S. Pat. No. 4,075,237 describes 1,4-dimethyl-2-hydroxystyrene, while U.S. Pat. No. 4,565,846 teaches the use of poly(3,5-dimethyl-4-hydroxystyrene). Japanese patent 84023747 describes anti-static compounds employing poly(acetoxymethylstyrene) and U.S. Pat. No. 4,221,700 describes a stabilized synthetic polymer composition using poly(alkylated alkenylphenol) including 2-methyl paravinyl phenol. U.S. Pat. Nos. 4,600,683 and 4,543,397 describe poly(alphamethyl vinylphenol). U.S. Pat. Nos. 4,517,028; 4,460,770 and 4,539,051 describe dimethylvinylphenol.
The preparation of 4-hydroxystyrene is well known in the art. One process is described in U.S. Pat. No. 4,316,995 and another is described in U.S. Pat. No. 4,451,676. Vinyl phenol may be prepared by a five step process of (1) acetylating phenol to p-hydroxyacetophenone, (2) acetylation of p-hydroxyacetophenone to p-acetoxyacetophenone, (3) hydrogenation of pacetoxyacetophenone to p-acetoxyphenylmethylcarbinol, (4) dehydration of p-acetoxyphenylmethylcarbinol to p-acetoxystyrene, and (5) saponification of p-acetoxystyrene to p-vinylphenol. This latter method is more fully described in Corson, B. B., et al, Preparation of Vinylphenols and Isopropenylphenols, J. Org. Chem., April 1958.
Known processes for the hydrogenation of 4-acetoxyacetophenone to 4-acetoxyphenylmethylcarbinol have been conducted with a Pd/C catalyst. This method has required the presence of such solvents as methanol and tetrahydrofuran. While this hydrogenation may be used in conjunction with the special dehydration process of this invention, it is a lesser preferred embodiment since the use of the solvent necessarily requires its ultimate removal. Problems which have been experienced include the dissolution of the 4-acetoxyacetophenone in the solvent; increased reactor volume due to the presence of the solvent; subsequent removal of the Pd/C catalyst from the large volume of solvent in the 4-acetoxyphenylmethylcarbinol mixture; separation of the solvent from 4-acetoxyphenylmethylcarbinol; purification and recycling of the solvent; solvent losses; and by-products from the solvent. The present invention most preferably employs a process wherein the solvent is completely eliminated. By this means it has been found that the selectivity of the reaction is substantially not adversely affected by the elimination of the solvent component. Also, other side reactions are not observed and an economical operation of the process is made possible.
This invention especially provides an improved method for dehydrating 4-acetoxyphenylmethylcarbinol. This is performed by heating at 85.degree. C. to 300.degree. C. under a vacuum of about 0.1 mm HgA to 760 mm HgA, preferably for about ten minutes or less and more preferably about two minutes or less in the presence of an acid catalyst. Conventional practice conducts this reaction in a batch reactor. Unfortunately, the batch process required about three hours. The present invention substantially improves (reduces) reaction time by employing a low residence time reaction. In addition, a reaction selectivity increase of at least about 10% is observed. In other words, the 4-acetoxyphenylmethylcarbinol is exposed to high temperatures for relatively short time periods for conversion into 4-acetoxystyrene, with a resultant improvement in the selectivity to 4-acetoxystyrene of at least 10% being obtained.